Plasma discharge is used for gas excitation for generating active gas including ions, free radicals, atoms, and molecules. The active gas is widely used in various fields, and is representatively used in processes such as etching, chemical vapor deposition (CVD), and asking in semiconductor manufacturing processes, for example.
FIG. 1 is a block diagram illustrating a general plasma power supply system. Referring to FIG. 1, a facility for generating plasma largely includes a plasma power supply 10 for supplying power, an impedance matching box 20 for supplying maximum power, and a plasma load 30. The plasma power supply 10 includes an RF generator that oscillates at a high frequency, and the impedance matching box 20 matches the impedance of an output terminal of the plasma power supply 10 with the impedance of the plasma load 30, for example, a load such as a processing chamber, which is not fixed and changed due to the kind of a process or a change in internal environments, thereby allowing desired high frequency power to be applied to the processing chamber.
Typically, the impedance of the output terminal of the plasma power supply 10 is fixed to about 50Ω, but the impedance of the plasma load 30 is variously changed. The impedance matching box 20 varies impedance according to a change in the impedance of a load to match impedance between the plasma power supply 10 and the processing chamber so as to reduce reflected waves from the plasma load 30, thereby preventing damage to the RF generator and allowing high frequency RF power to be completely used in the processing chamber without loss.
FIG. 2 is a circuit diagram illustrating the impedance matching box including a vacuum variable capacitor. Referring to FIG. 2, an inductor 41 and a tuning capacitor 42 are serially connected between the plasma power supply 10 and the plasma load 30, and a load capacitor 43 is installed between an input terminal of the inductor 41 and a ground. In general, the tuning capacitor 42 and the load capacitor 43 are varied to adjust impedance in a state in which the value of the inductor 41 is fixed, and each capacitor includes a vacuum variable capacitor (VVC).
A controller 40 provided in the impedance matching box 20 measures power inputted from the RF generator and power reflected from the plasma chamber and operates an operating mechanism that adjusts the position of the VVC, thereby performing impedance variable control. However, the position of the VVC, where impedance matching occurs, varies depending on the type of a semiconductor process, a process recipe, each process step and the like, and when the initial position of the VVC is erroneously selected, an area where impedance matching is not possible may occur and process fail may occur.
Furthermore, when there is a large deviation between the initial position of the VVC and the final position of the VVC where matching occurs, a time required for impedance matching may increase, power reflected from the chamber may increase at the initial stage of the process, and the continuity of the process may deteriorate.